After an oil well has been in operation for a time, its productivity often diminishes to a point at which the operation of the well is marginal or economically unfeasible. It is frequently the case, however, that substantial quantities of crude oil remain in the ground in the regions of these unproductive wells but cannot be liberated by conventional techniques. Therefore, it is desirable to provide methods for efficiently increasing the productivity of a well, provided it can be done economically. By way of definition the common meaning of borehole is merely a hole that is drilled into the surface of the earth, however once encased forms a production oil well for the purpose of extracting hydrocarbons. Notably, a borehole can serve as an injection or monitor well and in the case of the present invention allows for the insertion of a down hole seismic pressure wave generator.
A multiplicity of methods have been discovered for improving the oil recovery efficiency, yet large volumes of hydrocarbons remain in the oil rich formation after secondary, or even tertiary recovery methods have been practiced. It is believed that a major factor causing the retention of the hydrocarbons in the formation is the inability to direct sufficient pressure forces on the hydrocarbon droplets residing in the pore spaces of the matrix formation. Conventional oil recovery is accomplished in a two tier process, the primary or initial method is reliant on the natural flow or pumping of the oil within the well bore until depletion, once the free flowing oil has been removed a secondary means is required—where an immiscible fluid, such as water, is forced into an injection borehole to flush the oil contained within the strata into a production well. In the past it has not been cost effective to employ tertiary or enhanced oil recovery (also referred to as EOR) methods, albeit up to seventy percent of the total volume of oil may still remain in an abandoned oil well after standard oil recovery techniques are used.
Another technique that has been employed to increase the recovery of oil employs low frequency vibration energy. Low frequency vibration from surface or downhole sources has been used to influence liquid hydrocarbon recoveries from subterranean reservoirs. This type of vibration, at source-frequencies generally less than 1 KHz, has been referred to in the literature as sonic, acoustic, seismic, p-wave, or elastic-wave well stimulation. For example, stimulation by low frequency vibration has been effectively utilized in some cases in Russia to improve oil production from water flooded reservoirs. Examples from the literature also suggest that low frequency stimulation can accelerate or improve ultimate oil recovery. Explanations for why low frequency stimulation makes a difference vary widely, however, it is understood that the vibration causes the coalescence of oil droplets to re-establish a continuous oil phase due to the dislodging of oil droplets. Additionally it is believed that the sound waves reduce capillary forces by altering surface tensions and interfacial tensions and thereby free the droplets and/or enable them to coalesce. For example, U.S. Pat. No. 5,184,678 to Pechkov et al. issued Feb. 9, 1993 discloses a method and apparatus for stimulating fluid production in a producing well utilizing an acoustic energy transducer disposed in the well bore within a producing zone. However, Pevhkov only teaches that ultrasonic irradiating removes fines and decreases the well fluid viscosity in the vicinity of the perforations by agitation, thereby increasing fluid production from an active well.
Ultrasonic waves can improve and/or accelerate oil production from porous media. The problem with ultrasonic waves is that in general, the depth of penetration or the distance that ultrasonic waves can move into a reservoir from a source is limited to no more than a few feet, whereas low frequency or acoustic waves can generally travel hundreds to thousands of feet through porous rock. While sonic stimulation methods and apparatus to improve liquid hydrocarbon flow have achieved some success in stimulating or enhancing the production of liquid hydrocarbons from subterranean formations, the acoustic energy transducers used to date have generally lacked sufficient acoustic power to provide a significant pulsed wave. Thus, there remains a continuing need for improved methods and apparatus, which utilize sonic energy to stimulate or enhance the production of liquid hydrocarbons from subterranean formations. Acoustic energy is emitted from the acoustic energy transducer in the form of pressure waves that pass through the liquid hydrocarbons in the formation so that the mobility of the liquid hydrocarbon is improved and flow more freely to the well bore. By way of definition an elastic-wave is a specific type of wave that propagates within elastic or visco-elastic materials. The elasticity of the material provides the propagating force of the wave and when such waves occur within the earth they are generally referred to as seismic waves.
The increasing value of a barrel of oil and the increased demand for oil has created a greater interest in tertiary enhanced oil recovery methods to further oil availability by the revitalization of older wells, including those that have been abandoned due to a high ratio of water compared to the volume of total oil produced, or commonly called the water cut. The primary intent of enhanced oil recovery is to provide a means to encourage the flow of previously entrapped oil by effectively increasing the relative permeability of the oil embedded formation and reducing the viscosity and surface tension of the oil. Numerous enhanced oil recovery technologies are currently practiced in the field including thermodynamics, chemistry and mechanics. Three of these methods have been found to be commercially viable with varying degrees of success and limitations. Heating the oil with steam has proven be an effective means to reduce the viscosity, provided there is ready access to steam energy, and accounts for over half of the oil currently recovered. The use of chemical surfactants and solvents, such as CO2, to reduce the surface tension and viscosity, while effective, are not widely used due to cost, contamination and environmental concerns. However, seismic stimulation lacks any of the aforementioned limitations and is therefore being further explored as a viable enhanced oil recovery technique.
The vibration of reservoir rock formations is thought to facilitate enhanced oil recovery by (i) diminishing capillary forces, (ii) reducing the adhesion between rocks and fluids, and (iii) causing coalescence of the oil droplets to enable them to flow within the water flood. Recent studies at the Los Alamos National Laboratory conducted by Peter Roberts have indicated that this process can increase oil recovery over substantially large areas of a reservoir at a significant lower cost than any other enhanced oil recovery stimulation method. Accordingly, the systems and methods disclosed herein provide a low-cost tertiary solution for the reclamation of oil that had previously been uneconomical to retrieve. It is, therefore, a general object of the present disclosure to characterize downhole vibratory seismic sources capable of generating elastic-wave vibration stimulation within a previously abandoned oil field in order to extract the immobile oil. More specifically, by employing an apparatus for generating acoustic waves, oil recovery is stimulated within an oil deposit in fluid contact with a borehole into which the acoustic wave source can be placed. In one embodiment, the apparatus comprises: an elongated and generally cylindrical housing suitable for passing through a borehole, an accumulator; a pump, an energy transfer section, and a pressure transfer valve, wherein the pump pressure is stored within said accumulator and subsequently transferred, thereby releasing acoustic wave energy into the fluid surrounding the apparatus.
Accordingly, disclosed in embodiments herein is a system for imparting seismic wave energy within an oil reservoir in the form of a P-wave, having a controlled acoustic frequency, so as to alter the capillary forces of the residual oil.
In one embodiment herein there is disclosed a method for the controlled release of highly pressurized ambient fluids through opposed orifices of a rotary valve. As an alternative or additional configuration, seismic energy may be mechanically released by means of a dynamic isotropic transducer having a radial surface consisting of a plurality of adjacent longitudinal surfaces that are concurrently displaced by means of an associated set of radially configured pistons.
It is therefore an objective of the embodiments to provide a system for stimulating wells to increase the pressure and improve the flow of crude oil into the casings. It is a further object to provide an effective technique for removing deposits that clog the perforations of the oil well casing. It is yet another object of the disclosed embodiments to provide an apparatus wherein the resultant vibrational energy from the wave pulse generator is developed within the down hole apparatus by converting electro or mechanical-energy delivered from the surface into hydraulic energy. It is a still further object of the disclosed embodiments to provide such apparatus wherein a plurality of wave pulse generators may be controlled in a synchronized manner so as to provide a broad wave front and to thereby maximize the energy transfer within the oil strata. Other objects and advantages of the disclosed systems and methods will become apparent from a consideration of the following detailed description taken in conjunction with the accompanying drawings.
The various embodiments described herein are not intended to limit the embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the disclosure and appended claims.